升級 SQLAlchemy 2.0 之路 - Kenji Pa

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Basic stack: marshmallow + Werkzeug + SQLAlchemy

migration to 2.0 is too long

Why bother upgrating ?

Performance
- Nice to have… but not primany reason
Maintainability –> Yes, risk management
- 1.x will be deprecated eventually (main reason)
Better type checking support looks nice

Minimize impacts to the application
Application behaviour unaltered
- To ensure we can reason it on code-level:
- All changes must be lexically 1-to-1 mapped
- Things should always work before and after a commit (safely revertible)
Do not affect team development
- migration should not slow down team development velocity
When possible, always migrate iteratively
Non-goals: Refactor / bug fixes

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Tests never cover everything:
a. At one point we got all tests passed, but when we run the application, it's just dead

Implemented configuration to control these flags:
- So in case abnormal happens we could revert it back very quickly
Tuned out extremely smooth, likely because
- We have request-scoped & task-scoped session, app code rarely needs to manage sessions (commit/create sessions)






users = (
    session.query(User).filter().all()
)

stmt = select(User)
users = session.execute(stmt)

Pagenation
- Offset, limit, order by, total page, etc
- We happen to have a centralized place for all these queries
Performance reason
- Reporting / batch data processing where all is too slow

OLD:


session.query(User).filter_by(...).first()

NEW:





session.scalars(
    select(User).
    filter(...).
    limit(1)
).first()

Below is the part that speaker updated the talk/tutorial after speech
講者於演講後有更新或勘誤投影片的部份